For the ‘deformation under load’ part of the Drone Design Workshop, it is required to provide a y-direction fixed displacement restriction along with 2 symmetry planes to fully constrain the drone model for the simulation. This node should be at the intersection edge of the 2 planes to avoid overconstraining the model, but only faces and volumes are allowed for the fixed value constraint.

I would therefore like to know how to get around this problem as the simulation crashes without the proper constraints with a ‘Solution matrix not factorisable’ error.

# Is it possible to select a single node for a fixed value boundary condition?

**K_Timo_Eng**#1

**jousefm**#2

Hey @K_Timo_Eng and sorry for the delayed response!

Unfortunately that is not possible anymore but we could theoretically activate this for a specific mesh type but only if there is no other way to make your setup work otherwise. In your case you might also want to fix a specific face to constraint the degrees of freedom.

Best,

Jousef

**K_Timo_Eng**#3

Hello @jousefm,

Thanks for getting back to me.

I did try fixing other faces that are either normal to the symmetry planes and have no constraints in the prescribed direction, or away from the symmetry planes altogether, but this was to no avail either. I also can’t see any unconstrained rigid bodies in the model so I’m stuck here.

I also encountered a similar problem with result control, where I need to select an edge for an Edge calculation but can’t assign any entities as the entities picker won’t turn on, and the select edges feature says edges not allowed.

**jousefm**#4

Hey @K_Timo_Eng!

Do you have a project link so that I can have a look at that? Maybe I can find a workaround so that the tutorial can also be adapted before others run into the same troubles

Cheers and thanks for the heads up!

Jousef

**K_Timo_Eng**#5

Hello @jousefm,

My project link is as follows:

https://www.simscale.com/projects/K_Timo_Eng/drone/

I have also sent you an invite.

There are 4 simulations in the project. The one I am referring to here is named ‘Drone Arm Stress Analysis’.

The ‘Y restriction’ boundary condition is not fully set up in that simulation.